A fastening element with a cylindrical casing comprising an internal thread and provided with expanding elements is described in U.S. Pat. No. 4,133,245. Said fastening element which is insertable into the bore of a component also comprises flange-like extensions at its end opposite the expanding elements, which provide support in axial direction. In order to secure the fastening element by means of the expanding elements which are deformable in radial direction by turning a screw, an expensive bore is required which is countersunk from the rear of the component receiving the fastening element. Because of this the use of the fastening element in a so-called blind bore is not possible.
In addition, an expanding plug is known from DE-OS-30 05 437 which is cylindrical in form and has expanding elements at the end insertable into a bore, which are deformed in the direction of the longitudinal middle axis and expanded on inserting a specially formed expanding element and pressed against the bore walls in the prepared bore and thus secure the expanding sleeve. The disadvantage here is that for use as a fastening element an expanding element coordinating with the expanding plug that can be driven into the latter is required, and for adequate securing very high axial impact forces are necessary.
Furthermore, the expanding plug does not have any cutting extensions penetrating into the surrounding material, which means that sufficiently high holding forces cannot be obtained in the bore. As in addition there is no thread on the inner wall of the expanding plug and the expanding element has a smooth surface, it is possible that the expanding element will detach itself from the expanding plug in adverse conditions, and in this way the fastening cannot be maintained.
Furthermore, a fastening element or bolt anchor is known from U.S. Pat. No. 1,396,569 A which describes a metal blank or formed metal part comprising expanding elements. The expanding elements are connected by a strip-like flange, which has the same alignment as the expanding elements, whereby the said strip-like flange permits the rolling up of the metal section and thus an approximately cylindrical component is produced. The bolt anchor or the fastening element comprises thread-like elevations projecting over the outer casing, by means of which a securing of the bolt anchor is permitted in a bore surrounding the latter. The disadvantage of this design of fastening element is that it is not formed as a self-contained component and the fastening element can thus expand undesirably on inserting a bolt, or the inside diameter can increase unintentionally. Because of this undesired expansion of the fastening element the securing of a bolt inserted into the fastening element is influenced negatively and in an extreme case the connection of the bolt in the fastening element can become detached. Furthermore, the elevations arranged on the exterior of the expanding elements are not formed as cutting edges so that penetration into the material surrounding the fastening element is prevented, and thus there cannot be a form-closed fastening of the fastening element into the bore hole.